The present invention is directed to a prosthetic device that can be surgically implanted between the chest wall and lungs of a patient. The device has a bladder with a volume that can be adjusted by externally inserting or removing gas and is of particular use for emphysema patients that have undergone lung volume reduction surgery. In addition, the device can be used to provide respiratory support for patients.
Emphysema is a disabling disease that causes progressive and irreversible damage to lung tissue. It is the forth leading cause of death in the United States and a major cause of morbidity and mortality worldwide (Feinlieb, et al., Am. Rev. Respir. Dis. 140:s9-s18 (1989)). In its purest form, emphysema affects between 1.5 and 2 million Americans. However, the vast majority of the 12 million people in this country with disabling chronic obstructive pulmonary disease, including those with diagnoses of chronic bronchitis and asthma, also have a major component of disease related to emphysema. Thus, it is estimated that emphysema contributes to lung dysfunction in 6-8 million people in the U.S., and in many more individuals worldwide (Higgins, et al., in Clinical Epidemiology of Chronic Obstructive Pulmonary Disease, pp. 23-43, Marcel Dekker, New York).
It has been recently shown that respiratory function in emphysema patients can be improved by surgically resecting the most badly damaged regions of tissue (Cooper, et al., J Thorac. Cardiovasc. Surg. 109:106-119 (1995)). The technique, termed xe2x80x9clung volume reduction surgeryxe2x80x9d (LVRS), has become a preferred therapeutic option in patients with end stage disease (Ingenito, et al., N. Encl. J Med. 338:1181-1185 (1998); Martinez, et al., Am. J Resp. Crit. Care Med. 157:A497 (1998)). Unfortunately, the benefits derived from LVRS vary significantly from patient to patient and are lost over time. If a means can be found for post-operatively adjusting effective lung size without a need for further surgery, then LVRS could be performed more effectively and more safely in most patients and the long term benefits of LVRS should be greatly improved.
The present invention is based upon the development of a prosthetic device that can be implanted into the pleural cavity of patients for the purpose of improving respiratory function. The main characteristic of the device is that its volume can be adjusted through a subcutaneous port to improve the recoil of lung tissue and to thereby optimize the physiological benefits derived from lung volume reduction surgery.
In its first aspect, the invention is directed to the implantable prosthetic device itself. The device is comprised of a bladder and an attached connector tube. The bladder is made of material that is biocompatible, impermeable to gas and elastomeric, i.e., it should be non-rigid, and exert recoil pressure upon expansion. The bladder should fit snuggly within the pleural cavity between a patient""s lungs and their chest wall and be of a sufficient size to exert inward pressure on the lung when expanded. The outer surface of the device which rests against the chest wall will typically be coated with a lubricating biocompatible hydrogel to allow the chest wall to slide easily across the surface and prevent the formation of adhesions.
The bladder of the device has two chambers: an inner chamber formed by the lumen of multiple septated compartments; and an outer chamber, external to the septated compartments and internal to the inner surface of said bladder. The septated compartments are made of biocompatible gas-impermeable, elastomeric material and are interconnected to allow the exchange of gas. Upon inflation of the inner chamber of the bladder, the device assumes a crescentic shape that generally matches the contour of the pleural cavity. In a preferred embodiment, the bladder has multiple distinct lobes, preferably three, to help it adjust to different lung contours.
The connector tube, also made of biocompatible, elastomeric material that is gas impermeable, provides two separate passageways for gas, one to the inner chamber of the bladder and one to the outer chamber. For the purpose of the present invention, the end of the connector tube attached to the bladder is termed its xe2x80x9cdistal end.xe2x80x9d The other, xe2x80x9cproximal,xe2x80x9d end of the connector tube ends in two self-sealable ports, one for the passageway into the inner chamber of the bladder and the other for the passageway into the outer chamber. In a preferred embodiment, each sealable port is designed so that it is compatible with the introduction of gas or fluid using a syringe. The entire device must be suitable for surgical implantation. This means, among other things, that it must be chemically inert, non-immunogenic, and sterile. Preferred materials for constructing the device are silicone rubber, and polymers such as polypropylene and polyurethane. In general, the bladder of the prosthetic device should be 20-40 cm in diameter, each septated compartment should be 1-2 cm in diameter, and the connector tube should be 10-20 cm in length.
The outer chamber of the prosthetic device may also be connected to an oscillating pump to provide a means for reciprocally expanding and contracting the bladder. The pump is maintained outside of a patient""s body and is connected to the implanted device by means of a large bore needle inserted into the sealable port on the subcutaneously positioned connector tube. This arrangement is particularly preferred for providing breathing assistance to patients experiencing respiratory failure.
The prosthesis may be used in connection with a rigid deployment device to help in positioning the bladder after passing it through a mini-thoracotomy incision or during video-assisted thoracoscopic surgery. The deployment device has a handle attached to a retractable arm that extends through a surrounding sheath. Movable grasping prongs hold the ends of the bladder and are pivotally attached to the distal end of the retractable arm (i.e., the end that passes into the chest cavity of a patient) by means of a spring loaded hinge. This exerts pressure on the movable prongs, pushing them in an outward direction. At the end of the retractable arm opposite to the handle, there is a rounded cap that helps the device smoothly pass through a surgical incision. The sheath compresses the movable grasping prongs when the retractable arm is in its normal, retracted position. In order to open the prongs and thereby spread the bladder, the retractable arm is pushed through the sheath to an extended position in which the spring loaded hinge is outside the end of the sheath. As with the prosthesis, the deployment devise is constructed of material suitable for surgical use.
In another aspect, the invention is directed to a method of treating a patient for emphysema or respiratory failure by surgically implanting the prosthetic device described above. The bladder is positioned in the patient""s pleural cavity and the ports on the connector tube are positioned either at the surface of the patient""s skin or immediately under the skin. The ports provide a means for externally adjusting the volume occupied by the bladder within the patient""s pleural cavity. In a preferred embodiment, the device is implanted in emphysema patients that have undergone lung volume reduction surgery. Post-operatively, gas may be introduced or removed from the bladder in order to optimize the lung recoil of the patient. Thus, adjustments can be made in response to disease progression without the need for additional surgery. When used in this manner gas should be added to or removed from the septated inner chamber of the bladder.
In a preferred embodiment of the method, the prosthetic device is directly attached to the visceral pleural surface of a patient""s lung. Attachment of this nature helps to reduce air leaks that sometimes occur in patients that have undergone lung volume reduction surgery. Bonding is accomplished by coating the visceral pleural surface of the lung with thrombin and coating the surface of the prosthetic device that will contact the lung with a fibrinogen or a fibrin/collagen mixture. When the thrombin-coated lung surface makes contact with the fibrinogen-coated surface of the prosthetic device, a fibrin matrix is formed that holds the two surfaces together.
In addition, the present invention encompasses a method for providing respiratory assistance to a patient by surgically implanting the prosthetic device described above and then attaching it to an oscillating pump. In this embodiment, gas is cyclically pumped into and out of the non-septated outer bladder chamber. The pump is used to alternately inflate and deflate the bladder in order to support the patient""s breathing. Once a patient recovers to the point where assisted respiration is no longer needed, the device can be either removed or left in place after positioning the sealable ports for easy external access. In this manner, long term control over lung recoil can be achieved.